function u2h = fwr(uh)
    n = size(uh, 2) - 1;
    u2h = zeros(1, n / 2 + 1);
    u2h(1) = uh(1);
    u2h(end) = u2h(end);
    u2h(2:end-1) = (2 * uh(3:2:end-2) + uh(2:2:end-3) + uh(4:2:end-1)) / 4;
end